The International Monetary Fund on Sunday strongly backed the European Central Bank's plan to staunch the eurozone debt crisis with unlimited bond purchases, saying it was ready to get involved in designing and monitoring its implementation.

IMF Managing Director Christine Lagarde also said large, debt-strapped eurozone countries Spain and Italy had taken enough action to repair their finances to merit aid from the rest of the European currency union.

But, amid pressure on Madrid to request a full European bailout, Lagarde left open the scale of the IMF's possible involvement in ECB head Mario Draghi's plan, which was approved by the central bank's policymaking council on Sept 6.

Under the Draghi plan, the ECB would stand ready to buy any amounts of sovereign debt with a term of up to three years, thereby ensuring a government's access to funding, in return for a bailout deal with tight strings attached.

"What the central bank has announced last Thursday is a clear indication of the framework in which it would be an active player in restoring the situation in the eurozone," Lagarde told reporters in the Russian port city of Vladivostok after an Asia-Pacific summit.

Reuters